Problem: 9 binders cost $9.45. Which equation would help determine the cost of 3 binders?
There are several equations that could help determine the cost, each with a slightly different approach. If we let $x$ represent the cost of 3 binders, we have the following proportion: $\dfrac{x}{3}$ We have to pay $9.45 for 9 binders, and that can be written as a proportion: $\dfrac{\$9.45}{9}$ Since the price per binder stays the same, these two proportions are equivalent. $\dfrac{x}{3} = \dfrac{\$9.45}{9}$